In the Saw movies Jigsaw is poor guy, so how he could purchase all the materials and equipment required to build traps?
Some traps are very heavy and Jigsaw is cancer patient, so how did he build traps himself? And, if he used some help, how did he afford to pay their salaries?
Traps were built into houses, and houses cost a lot of money. How could he purchase all those houses?
Some traps are very sophisticated and would require very sepcial equipment to be built, not something that a poor cancer patient can purchase.